This invention relates to a novel derivative of the antibiotic spiramycin I, and more particularly to 3, 3", 4"-tri-O-acylspiramycin I represented by the formula (I): ##STR2## wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different groups, and at least one of the groups is a straight or branched chain alkylcarbonyl group represented by --COC.sub.m H.sub.2m+1, wherein m is an integer of 2-4, and the other group(s) are straight or branched chain alkylcarbonyl group(s) represented by --COC.sub.n H.sub.2n+1, wherein n is an integer of 1-4, which will be hereinafter referred to as "Compound (I)", and its pharmacologically acceptable acid addition salts.
Spiramycin is an antibiotic which is classified as a 16-membered, macrolide antibiotic and has a remarkable antibacterial effect on Gram-positive bacteria and mycoplasma. Owing to differences in substituents in the 3-position, spiramycin I (hydroxyl group in the 3-position), spiramycin II (acetyloxy group in the 3-position) and spiramycin III (propionyloxy group in the 3-position) are known as spiramycin.
Heretofore, the O-acetyl derivative of the spiramycin mixture, which is considered as a mixture of the 4"-O-acetyl derivative and the 3", 4"-di-O-acetyl derivative wherein when the substituent in the 3-position is a hydroxyl group, the hydroxyl group is also acetylated, is known [Chemical Abstracts vol. 75, 88896d, 74512p (1971)]. The O-acetyl derivative of the spiramycin mixture is commonly called "acetylspiramycin", adopted in the Japan Pharmacopoeia X, and widely used for therapeutic purposes. Further, though GB1158396A discloses 3, 3", 4"-tri-O-acetylspiramycin I as obtained, it is presumed from the described method for the production that the preparation contains considerable amounts of by-products such as diacetyl derivatives.
Further, it has been known that the 3", 9-di-O-acetyl compound of midecamycin [J. of Antibiotics 29, 536 (1976)] and the 3"-O-propionyl compound of leucomycin A.sub.5 (Japanese Published Unexamined Patent Application No. 148793/1979) have a better in vivo activity and reduce bitterness, compared with their starting compounds.